JP3507278B2 - Electroplating method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plating method for performing nickel electroplating mainly on electronic parts and steel plates using a so-called sulfamic acid plating bath, and particularly, it has a capability of suppressing sulfamic acid decomposition. The present invention relates to a plating method using an anode composed of the above insoluble metal electrode.

[0002]

2. Description of the Related Art A plating solution containing sulfamic acid is usually used for nickel plating of electronic parts such as electronic parts which require particularly high precision. This is because, when this plating solution is used, not only the plating throwing power is good and it is suitable for precision plating, but also chlorine ions, which are highly corrosive, do not remain in the plating film.

In nickel plating using a plating solution containing sulfamic acid, nickel metal is usually used as an anode. Nickel metal is a so-called solubility in which nickel gradually dissolves in the solution as the plating progresses. Form the anode. Since such an anode is used at the dissolution potential of nickel, there is no decomposition of other components in the plating solution,
Nickel ions in the plating solution are reduced by plating on the surface of the cathode material, but the reduced nickel ions are said to be replenished from the anode.From these points, the nickel electrode serves as the anode. Was considered the most desirable.

[0004]

However, even such a soluble anode has the following problems in reality. That is, when the current density becomes high, passivation occurs on the surface of the nickel anode, and smooth dissolution of nickel in the plating solution cannot be expected. In addition, the current flows through the passivation layer, which increases the overvoltage at the anode. That is, the resistance loss becomes large, and various problems occur.

That is, in this case, the plating voltage (bath voltage) becomes high. There is a problem that the sulfamic acid in the plating solution is decomposed remarkably due to the increase in the plating voltage due to the increase in the overvoltage, which makes it difficult to operate the plating normally. Furthermore, since the rate of generation of passive bodies is not constant,
There was also a problem that it was difficult to control the components of the plating solution because the amount of nickel eluted from the anode changed. Furthermore, if the passivation film falls off in the plating solution, slime is generated, and the slime is co-deposited on the nickel electrodeposition film, causing a product defect. Anode bags are often used to avoid the co-deposition of slime on the nickel electrodeposition coating, and doing so dissolves nickel from the nickel anode and replenishes it in the plating solution. Things will be difficult. After all, there was a problem that the plating operation had to be stopped at regular intervals and a complicated operation of replenishing the nickel anode had to be performed.

In order to solve these problems, it has been attempted to use a platinum-plated titanium electrode which is an insoluble electrode for the anode. Since the platinum-plated titanium electrode is insoluble, there is no problem that the distance between the electrodes is increased due to the formation of slime or the dissolution of the electrode itself. However, when nickel plating is performed using an insoluble electrode, the anodic reaction is an oxygen generation reaction, and therefore the anodic potential becomes high. In addition to this, when a platinum-plated titanium electrode is used, the oxygen overvoltage is as high as 600 to 800 mV, so the anode potential added with this becomes even higher.

Therefore, in this case, not only the electrolytic voltage rises but also the decomposition of organic substances such as sulfamic acid in the plating solution is accelerated. Since the potential is even higher, when nickel chloride is contained in this type of plating solution, chlorine ions are dissociated, and a part thereof is discharged as chlorine gas. When chlorine gas is discharged, there is a problem that the strong oxidizing action accelerates the decomposition of organic substances in the plating solution, which causes corrosion of the plating tank. Further, there is a problem in that the platinum-plated electrode is greatly worn out and has a short life in a plating solution containing organic substances and chlorine ions.

The present invention has been made in order to solve the above-mentioned problems, and is particularly excellent in corrosion resistance and durability in a nickel plating solution containing sulfamic acid, and even when operating at a high current density, sulfamic acid is used. It is an object of the present invention to provide an electroplating method using an anode that is less likely to decompose and can be stably operated for a long period of time.

[0009]

The present invention has solved the problem by the following means. (1) When electroplating nickel using a plating bath containing sulfamic acid, an insoluble metal electrode having an electrode catalyst layer mainly composed of iridium oxide and the balance being tantalum oxide or tin oxide is used as an anode. And the electroplating method. (2) The insoluble metal electrode is characterized by forming an oxide-coated electrode catalyst layer of iridium oxide of 60 to 90 mol% and the balance of tantalum oxide or tin oxide on a titanium base material. The electroplating method according to (1) above.

(3) The insoluble metal electrode is characterized in that the oxide-coated electrode catalyst layer is produced by a thermal decomposition method from a solution containing an iridium salt and a tantalum salt or a tin salt. The electroplating method according to (1) or (2). (4) The electricity according to any one of (1) to (3), wherein a contact between the anode and the plating solution is suppressed by providing a porous diaphragm on the surface of the insoluble metal electrode. Plating method. (5) The electroplating method according to (4), wherein the porous diaphragm is made of an insulating material containing silica.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described. In the case of the present invention, the base material of the anode provided in the plating solution is preferably titanium in principle. The titanium base material has a plate shape,
It may have a rod shape, an expanded shape, a perforated plate shape, or the like.
It is desirable that the surface of the base material is subjected to grid blasting or shot blasting so that the actual surface area is as large as possible.

The surface of the base material is coated with an electrode material which constitutes an insoluble anode catalyst layer, and is formed, for example, by coating and thermal decomposition. The following complex oxides are used as the insoluble anode material. Specifically, a composite oxide of iridium oxide and tantalum oxide or a composite oxide of iridium oxide and tin oxide is used. The composition ratio of iridium oxide is 50 mol% or more in the whole composite oxide, preferably 60 to 90.
It is good to set it as mol%. If the composition ratio of iridium oxide is less than 50 mol%, the oxygen generation overvoltage may increase, possibly because the number of reaction points as an electrode decreases, which may accelerate the decomposition of organic substances, which is not preferable. .

Moreover, when the plating solution contains nickel chloride, the catalytic action for the chlorine generation reaction is not so impaired even if the proportion of iridium oxide is small.
However, since the oxygen generation overvoltage increases, the chlorine generation reaction may be relatively promoted, which is also not very preferable. Further, when the composition ratio of iridium oxide is more than 90 mol%, the overvoltage of oxygen generation also becomes high in this case as well, and when nickel chloride is contained, the chlorine generation reaction is accelerated, which is not preferable.

The thermal decomposition method is the most suitable method for producing such an insoluble metal electrode. The thermal decomposition method is a method of applying a solution containing a metal salt that constitutes the electrode material onto a base metal,
This is a method of thermally decomposing this in air at 450 ° C to 650 ° C. In addition to the thermal decomposition method, for example, a method such as a sol-gel method in which an oxide or hydroxide is previously supported on an electrode substrate by using a binder or the like, or reactive PVD
There is a method of coating with a (vacuum vapor deposition) method or a CVD (chemical vapor deposition) method. There is no particular problem with these other than thermal decomposition method,
Probably because the crystallinity of the coating is generally good except for the thermal decomposition method and it is chemically stabilized, an insoluble metal electrode using a manufacturing method other than the thermal decomposition method generates oxygen when used as an anode in the plating solution. Tends to increase the overvoltage of. Therefore, it tends to accelerate the decomposition of organic substances, and if possible, it is preferably formed by a thermal decomposition method.

A porous diaphragm may be attached to the surface of the insoluble metal electrode for the purpose of preventing diffusion of organic substances and chlorine ions. The membrane attached to the surface of the insoluble metal electrode may be a membrane such as a so-called filter cloth, but a porous insulating layer or the like may be provided by a method such as thermal decomposition. For example, using water glass or silica, provide a porous thin coating film with insulation and corrosion resistance,
It is preferable to suppress contact between the anode and the plating solution.

In order to prevent slime in the plating solution due to elution or disintegration of the electrode material, the electrode in the plating solution is required to have sufficiently high corrosion resistance. An electrode in which an all-metal surface is coated with an electrode material containing a platinum group metal oxide, so-called DSE, has extremely high durability and is optimal for achieving the object of the present invention. The present invention is intended to solve the conventional problems by using an electrode whose characteristics, particularly electrochemical characteristics, are matched with the object of the present invention.

In the present invention, of the DSE type electrodes, stable iridium oxide which is not affected by the oxygen generation reaction is used as the main electrode catalyst substance, so that the anode has sufficient durability as an insoluble metal electrode. Furthermore, in order to minimize the decomposition of organic substances such as sulfamic acid in the plating solution, keep the anode potential as low as possible, and if possible, minimize the chance of these organic substances coming into contact with the anode surface. is necessary. Further, when chlorine ions are contained in the plating solution, it is necessary that the oxygen generation potential is low and the chlorine generation overvoltage is as large as possible in order to oxidize the chlorine ions and not generate chlorine. The present invention, as a result of intensive studies mainly on the iridium oxide electrocatalyst material, it was found that a complex oxide of iridium oxide and tantalum oxide, and a complex oxide coating of iridium oxide and tin oxide are the most suitable. It was found that the desired characteristics could be obtained by specifying the composition, and it was completed.

A porous diaphragm may be attached to the surface of the insoluble metal electrode for the purpose of preventing diffusion of organic substances and chlorine ions. When a corrosion-resistant coating such as an insulating thin layer of water glass or porous silica is provided on the electrode surface, the decomposition of sulfamic acid, which is the diffusion-controlling agent, and the generation of chlorine gas can be further suppressed.

[0019]

EXAMPLES Examples will be described below, but it goes without saying that the present invention is not limited thereto. (Examples 1 to 10) The surface of a titanium base material (50 x 50 mm) was grid-blasted and pickled with hot oxalic acid. After that, iridium chloride and tantalum chloride, and iridium chloride and tin chloride are dissolved in each hydrochloric acid solvent,
A metal salt solution having a concentration of 100 g / liter in terms of metal was obtained. The metal salt solution thus obtained is applied to the surface of the titanium substrate, which is then applied at 100 ° C. for 10 hours.
After drying for 1 minute, heat treatment for 20 minutes in an electric furnace at 500 ° C gives iridium oxide (60-90 mol%)
And tantalum oxide (40-10 mol%) and tin oxide (4
A catalyst layer composed of 0 to 10 mol% of mixed oxide was obtained on the surface of the titanium substrate.

The following application of the metal salt solution, drying and heat treatment were repeated to prepare the following insoluble metal electrode. That is, the ratio of iridium oxide is 60, 70,
80, 90 mol% and correspondingly, an insoluble metal electrode having an electrode material layer having a tantalum oxide ratio of 40, 30, 20, 10 mol%, or a tin oxide ratio of 40, 30 instead of tantalum oxide. , 20, 10 mol%
Each insoluble metal electrode having an electrode material layer that becomes The amount of iridium oxide alone is 15g / m
²

The prepared insoluble metal electrode was used as an anode material for electroplating in Examples 1 to 8, respectively. Separately, an insoluble metal electrode having an electrode catalyst layer having an iridium oxide content of 70 mol% was processed as follows. That is, about 10 g / m ² of silica was applied to the surface of the electrode catalyst layer for those containing tantalum oxide or tin oxide as the balance. The application of silica was performed by applying water-soluble colloidal silica on the surface in advance and drying it in an oven at 150 ° C. for 20 minutes. The one coated with silica was used as an anode material for electroplating in Examples 9 and 10.

On the other hand, an electrode was prepared by forming an electrode catalyst layer having an iridium oxide content of 100% on a titanium substrate in the same manner as in the above-mentioned example, and in Comparative Example 1, this was used as an anode for electroplating. Used for wood. Also, 30 mol of iridium oxide
%, Tantalum oxide, or 70 mol% of tin oxide, an electrode having an electrode catalyst layer made of each mixed oxide was prepared, and this was used as an anode material for electroplating in Comparative Examples 2 and 3. The amount of iridium oxide deposited was 15 g / m
² Further, a commercially available platinum-titanium electrode having a platinum coating thickness of about 3 μm was prepared and used as an anode material for electroplating in Comparative Example 4.

Each of the electrodes prepared as described above was used as an anode for electroplating as follows. That is, from the cathode of the copper plate (50 x 50 mm) to the electroplating tank,
It was mounted as an anode at a position separated by mm. Nickel sulfamate 300 g / liter, nickel chloride 30 g /
A synthetic nickel plating solution containing liter and 30 g / liter of boric acid was placed in an electroplating bath to obtain an anode current density of 20.
Electroplating was performed at A / dm ² and a liquid temperature of 50 ° C. for 1000 hours. The cathode was periodically replaced, and nickel ions consumed in the plating solution were replenished by adding nickel hydroxide salt.

The electroplating was carried out for each anode material for 1000 hours, and after the completion, the sulfate ion concentration in the plating solution was analyzed by the barium sulfate gravimetric method and converted into the decomposition rate (%) of sulfamic acid. In addition, the consumption rate (%) of the electrode catalyst was measured by a fluorescent X-ray analyzer (Rigaku Denki Co., Ltd./3511-S).
It was determined by the calibration curve method of. Table 1 shows the results of the plating treatment for each electrode as the decomposition rate of sulfamic acid and the consumption rate of the electrode catalyst.
It was shown to.

[0025]

[Table 1]

From Table 1, it was found that in Examples 1 to 8, the decomposition rate of sulfamic acid was 16 to 22% and the catalyst consumption rate was 3 to 7%. Furthermore, in Examples 9 and 10, both the decomposition rate of sulfamic acid and the exhaustion rate of the catalyst were further reduced to 2%. On the other hand, in the comparative example, the decomposition rate,
The wear rate was large, and particularly in the comparative example using the platinum-plated titanium electrode, both the decomposition rate and the wear rate were extremely large.

When each electrode used in this example was used as an anode of a nickel plating solution containing nickel sulfamate as an electrolyte, the oxygen generation potential was reduced by about 300 mV as compared with a platinum-plated electrode, and the decomposition rate of sulfamic acid was decreased. (%) Could be reduced to 1/3 or less. Further, the consumption rate (%) of the catalyst can be reduced to 1/8 or less of that of the platinum-plated electrode, which enables stable plating operation for a long period of time.

[0028]

The electroplating method of the present invention uses an insoluble metal electrode in which the surface of the anode material is mainly composed of an electrode catalyst layer, that is, iridium oxide, and which is covered with an electrode catalyst layer containing tantalum oxide or tin oxide. Enables stable plating operation over a long period of time. In particular, decomposition of organic substances such as sulfamic acid is small, and chlorine is practically hardly generated even when nickel chloride is contained in the plating solution. It has excellent corrosion resistance and durability, and even when it is operated at a high current density, slime, etc. are practically scarcely generated. The contamination of the plating solution is extremely small, and it is most suitable for applications that require precision, such as plating of electronic parts.

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-6-122988 (JP, A) JP-A-62-103387 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C25D 17/10 101 C25D 3/12 102 C25D 17/12

Claims (5)

(57) [Claims] 1. When performing electroplating of nickel using a plating bath containing sulfamic acid, an insoluble metal electrode having an electrode catalyst layer mainly composed of iridium oxide and the balance being tantalum oxide or tin oxide is used as an anode. And an electroplating method. 2. The insoluble metal electrode is formed by forming an oxide-coated electrode catalyst layer containing iridium oxide of 60 to 90 mol% and the balance of tantalum oxide or tin oxide on a titanium base material. The electroplating method according to claim 1, which is characterized in that. 3. The insoluble metal electrode is characterized in that the oxide-coated electrode catalyst layer is produced by a thermal decomposition method from a solution containing an iridium salt and a tantalum salt or a tin salt. The electroplating method according to claim 1 or claim 2. 4. The electroplating according to claim 1, wherein a contact between the anode and the plating solution is suppressed by providing a porous diaphragm on the surface of the insoluble metal electrode. Method. 5. The electroplating method according to claim 4, wherein the porous diaphragm is made of an insulating material containing silica.